Welcome to Avian Flu Watch: Global H5N1 Tracker. Today, we offer a scientific, data-driven update on the global battle with highly pathogenic avian influenza H5N1.

Worldwide, the H5N1 virus continues to pose a grave threat, disrupting poultry production and crossing into new species and regions. According to the World Health Organization, as of April 2025, there have been 973 confirmed human H5N1 cases and 470 deaths in 25 countries – a fatality rate of 48 percent. Outbreaks since 2020 have surged due to the rapid global spread of clade 2.3.4.4b, affecting birds, mammals, and occasionally humans.

Let’s break down the latest regional hotspots and case numbers. In North America, the US West Coast remains a primary epicenter among cattle, with mathematical modeling from Nature indicating high herd positivity rates in California, Oregon, and Washington through late 2024 and early 2025. Arizona and Wisconsin now stand at heightened risk. In Mexico, the first fatal human H5N1 case was recorded in April 2025. Canada saw its latest severe human case in late 2024; British Columbia experienced mass outbreaks among poultry.

In South America, Brazil declared multiple states of emergency since 2023 due to wild bird outbreaks and continues intense surveillance across major poultry regions. The Pan American Health Organization confirms that by May 2025, 14 countries and territories have reported outbreaks in animals, especially in the Americas.

Across Asia, China remains a hub with routine detection of H5N1 in live poultry markets along migratory bird flyways, notably in Jiangsu, Shandong, and Henan provinces. Southeast Asia saw fresh clusters in Cambodia and Vietnam, with Cambodia reporting three fatal human cases in early 2025.

Europe has recently seen new human infections in the UK and persistent outbreaks in poultry. The Middle East data highlights Turkey and Lebanon as crossroads for cross-border transmission in birds, further linked to genetic flows between Egypt and Israel.

Visualizing trend lines, H5N1 cases in poultry and wild birds have surged since late 2023, peaking in early 2024 in the US and China, then oscillating as containment strategies took partial effect, illustrated by steep rises and intermittent drops in ‘Our World in Data’ case curves. Comparative statistics show that clade 2.3.4.4b dominates global outbreaks, but reassortant strains are emerging, including hybrids in Southeast Asia with genes from older lineages, raising concerns over future adaptability and transmission.

Analysis of cross-border transmission reveals wild bird migratory flyways, trade routes in poultry, and movement of livestock as the main factors in viral spread. Interventions like testing cattle prior to export in the US, and poultry export bans in the Philippines and other nations, have had some effect but succeeded only in partially quelling transmission. Migratory birds continue to seed new outbreaks across continents, evidenced by cases in Antarctica, the Arctic, and the Americas.

Notable containment successes include swift culling campaigns in the US and emergency operations in Brazil. However, failures are apparent in regions where surveillance lags or biosecurity measures remain insufficient, such as continued livestock outbreaks in US dairy herds and recurring farm infections in South and Southeast Asia.

Emerging variants of concern include the bovine-origin US strains showing divergence from East Asian bird-origin viruses, and the Greater Mekong Subregion’s recent hybrids which mix genes from multiple global clades. These may complicate future vaccine and diagnostic efforts.

Travel advisories currently recommend heightened avoidance of live poultry markets in Asia, restriction of handling sick or dead birds, and compliance with local health and agriculture advisories for travelers to outbreak zones. Animal health agencies urge...